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Aluminum Electrolytics
Aluminum electrolytic capacitors (ALUMINUM
LYTICS) are the easiest capacitor type to identify. They
are most commonly cylinder shaped and have radial or
axial leads. Large value aluminum lytics often have
screw terminals or solder lugs. The case of an aluminum
lytic usually is rolled in or formed out near the lead end
to hold the end cap and seal. All aluminum lytics have a
seal that is soft and rubber like to allow gasses to vent.
Depending on the physical size of the case, the soft seal
may make up the entire end of the case, or it may be just
a small section of a hard end cap. Aluminum lytics have
the largest physical size to capacity ratio of all capacitor
types. These capacitors may also have several sections,
with each section having a different capacitance value
but sharing the same negative terminal, usually the case.
This is unique to aluminum electrolytics, and whenever
you encounter a capacitor having several different
capacitance value sections, it will be an aluminum
electrolytic.
Because of their unique physical characteristics, most
aluminum lytics usually aren't easily confused with other
capacitor types. Axial lead aluminum lytics, however,
may possibly be mistaken for axial lead tantalum lytics.
The lead weld is an identifying characteristic of the
tantalum in electrolytic and is a quick way to
differentiate between an axial lead aluminum lytic and a
tantalum lytic. Aluminum lytics do not have a lead weld
on either terminal.
In addition, surface mount aluminum electrolytic
capacitors are becoming increasingly popular. They
resemble leaded aluminum lytics in their shape but are
much smaller and have very short legs for mounting.
Surface mount aluminum lytics can fail in all of the
same ways as a standard size capacitor.
Fig. 21: Various types of aluminum electrolytic capacitors.
Tantalum Electrolytics
Dipped tantalum electrolytics are replacing aluminum
lytics in many electronic circuits. They have less leakage
and higher value tolerances than aluminum lytics.
Tantalum electrolytic capacitors are about one-half the
size of a similar aluminum electrolytic of the same value
and voltage rating.
While they may have many shapes, tantalum capacitors
always have polarized leads. Lead polarization is often
the only way to distinguish a tantalum lytic from another
type of capacitor. Once you become familiar with the
polarity markings used, tantalum lytics are not difficult
to identify. The polarity markings are not meant to be
difficult to notice or understand, although if you are not
aware of them, they might be overlooked. Pay careful
attention so that you do not overlook the polarity
indication and misidentify a tantalum capacitor as
another type.
The simplest and most common polarity indicator is a
“+” sign near one of the leads. This is often used along
with a second type of indicator. In addition to the “+”
sign, each capacitor shown has a second indication of the
“+” lead: a lead weld, a tapered case, a rounded corner, a
line, or an extra ridge near the “+” lead.
A "+" indicator is not printed on all tantalum capacitors.
In many cases the polarity indicator will simply be the
lead weld, a tapered case or rounded corner, a line, or an
extra ridge on the case. Several other polarity identifiers
are also used. The end or side nearest the plus lead may
be painted one color. Also at times, just a dot or a line on
the side of the package will be used.
NOTE: Tantalum capacitors may use dots or stripes to
indicate value or tolerance. Do not confuse the value
color code for the polarity indicator of a tantalum
capacitor. The polarity indicator will be larger and
isolated from the color code.
Tantalum capacitors are also available in the small
surface mount or “chip” type. Tantalum chip caps could
be confused with the ceramic chip cap, since they are
similar in size and appearance at first glance. But, a
tantalum chip capacitor is polarized and has an easily
identifiable positive lead. The polarity identification that
may give you the most difficulty in identifying a
tantalum capacitor is lead length. The only identification
of the positive lead on some tantalum capacitors is that it
is longer than the other lead. Of course, this presents no
problem when the capacitor is new, but once it has been
installed into a circuit board, the leads are cut off to the
same length. In this situation, use the circuit as the clue
to the cap's type and polarity.
Fig. 22: Various types of tantalum electrolytic capacitors.
